Extrusion mandrel and method

ABSTRACT

An improvement in an extrusion mandrel in combination with the cylindrical part of the mandrel that defines the interior contour of the extruded workpieces which includes a short front member of generally cylindrical configuration but having a cross-sectional diameter and a length less than the cylindrical part and a base member joining the front member to the cylindrical part. In use, the mandrel is positioned so that the short front member always cooperates with the die at the beginning of the extrusion.

United States Patent [72] Invent gm f i' [56] References Cited [21] APPL No. 71 41 UNITED STATES PATENTS [22] Filed Apr. 3, 1968 3,116,834 1/1964 Hoffmann 72/260X [45] Patented May 25, 1971 941,365 11/1909 Hine 72/273X [73] Assignee Compagnle' Du Filage Des Metaux El Des FOREIGN PATENTS 957,465 5/1964 Great Britain e 9,025 6/1906 Great Britain 72/264 Primary Examiner-Charles W. Lanham Assistant Examiner-Robert M. Rogers AttorneyWebb, Burden, Robinson & Webb ABSTRACT: An improvement in an extrusion mandrel in [54] AND METHOD combination with the cylindrical part of the mandrel that g g defines the interior contour of the extruded workpieces which [52] US. 72/264, includes a short front member of-generally cylindrical configu- 72/370, 72/273 ration but having a cross-sectional diameter and a length less [51] Int. Cl ..B2lc 23/04, than the cylindrical part and a base member joining the front B21c 25/00, B2lb 17/02 member to the cylindrical part. In use, the mandrel is posi- [50] Field of Search 72/264, tioned so that the short front member always cooperates with 266, 273; 207/19 (Mandrals); 72/370 the die at the beginning of the extrusion.

Patented May 25, 1971 3,580,038

INVENTQR. Jean-Michel Andreassian F I g. 3 BY WM, BWMQOLCWW 0 MM HIS ATTORNEYS EXTRUSION MAN DREL AND METHOD My invention relates to a novel extrusion mandrel and a method of extruding using the mandrel. Specifically, my invention provides a novel mandrel in which the cylindrical extrusion defining member has a frontal member of lesser crosssectional diameter that permits extrusion at higher velocities for a greater period of time.

The extrusion of steel, other metals and alloys difiicult to deform into tubes and other hollow sections is made more profitable as the hourly output is increased. Efforts to increase the hourly output have been directed to increasing the number of pushes per hour by reducing the work cycle of the press. Efforts, however, have not been directed to increasing the weight of the metal transformed in one push. This has been due primarily to the fact that, when making a given product by extrusion from a press with a given force, neither the length nor the diameter of the billets can be increased.

The length of an extruded tube is proportionate to its runout velocity and the duration of the extrusion. Until now, the lubricating medium has not permitted obtaining velocities higher than 6 to 8 meters per second (18-25 feet per second). Furthermore, because of die wear the duration of the extrusion itself has been limited to 3 to 4 seconds, which meant that tubes exceeding 25-30 meters (80-100 feet) in length could not be economically produced. Moreover, a press with a given force utilizing a mandrel of a given diameter required that the container diameter be limited so that pressure was available at least equal to the maximum pressure required by the extrusion when starting and running the process.

When a glasslike lubricant is placed between the billet and the die, and between the billet and the container, as taught by French Pat. No.'966,733, the running pressure is quickly attained and held during the entire operation. However, it has been found that there exists, subsequent to startup, a brief period of time in which the pressure exceeds the running pressure or value by 20-40 percent. This means then, that the entire available force is not used during the running operation and that there is energy wasted in increasing the heat of the pressure transmitting liquid.

I have conducted studies to determine the pressures involved during the glass-lubricated extrusion of steel. FIG. I, in which the abscissa represents ram travel distance and the ordinate shows the pressure involved, is a record of such a test. The increased pressure or overpressure is that shown at point A.

The phenomenon of overpressure not only wastes energy but also causes the mandrel to deviate from the axis of the press, creates an uneven compression of the lubricating disc, causes a detrimental erosion of the tools, and is responsible for fatigue of the hydraulic valves and piping. An attempt has been made to avoid these drawbacks by slightly tapering the front end of the mandrel into a short frustum. This requires, however, an accurate positioning of the mandrel so that the front end of the frustum cooperates with the entry of the die bearing land at the beginning of the actual extrusion regardless of the length of the billet, the thickness of the lubricating disc, and the ram travel during compression prior to extrusion. If the condition of accurate positioning is not met, the starting extrusion ratio and, consequently, the starting extrusion pressure are unknown. Furthermore, and more importantly, the accurate positioning required is inconsistent with high operating speeds and high tonnage yields in industria1 operations. Additionally, such a design deprives the extruded product of the initial inside guiding usually afforded by a mandrel extending significantly beyond the die.

My invention pennits the avoidance of the undesirable overpressure without requiring the precise positioning required of the prior art mandrels. My mandrel has an elongated section which has a cross section conforming-to the inside configuration of the extruded product, a short frontal member having a cross section smaller than the cross section of the elongated part and a base element, such as a short frustum connecting the frontal member to the elongated part. To overcome the drawbacks referred to above, this mandrel is positioned in operation so that part of the short frontal element cooperates with the die at the beginning of the extrusion.

In the accompanying drawings, I have shown one preferred embodiment of my invention, in which:

FIG. 1 is a graph representing overpressure and running pressure without the use of my mandrel;

FIG. 2 is an axial view of my mandrel;

FIG. 3 is a partial section of a die and billet and an axial view of my mandrel initially positioned within the die; and,

FIG. 4 is a graph similar to FIG. 1 showing the elimination of overpressure with the use of my mandrel.

As shown in FIG. 1, overpressure A exists shortly after the beginning of the extrusion process. This overpressure can be eliminated by the use of my novel extrusion mandrel. As shown in FIG. 2, my mandrel comprises an elongated part 1 which defines the inside contour of the extruded product by traveling through the die. A short frontal member 3 is attached to part 1 by a base element 2. The cross section of frontal member 3 is smaller than the cross section of elongated part I. Preferably, member 3 blends into part 1 by base 2 comprising a short frustum.

As shown in FIG. 3 at the beginning of the extrusion process, member 3 is placed within the zone of die 4 prior to extrusion of billet 5. If the diameters of the cylindrical part 1 and of the aperture of die-4 had been preselected for extruding a member with a wall thickness e, when hot, it is apparent from FIG. 3 that when starting extrusion will produce a tube having a wall thickness E, which is larger than e perfectly defined, provided that member 3 initially cooperates with the die.

FIG. 4 shows a record of the pressure under such conditions as stated above. It can beseen that the starting pressure A has been so reduced as not to exceed the pressure required for the running of the extrusion process. This was achieved by selecting the wall thickness E so that the logarithms of the extrusion ratios corresponding to the production of wall thicknesses e and E are in proportion respectively with the overpressure A and the running pressure stated in FIG. 1. Under such conditions, the container diameter may be increased on a press with a given force.

To further explain the selection of E, it is readily recognized from FIG. 4 that the diameter (1) of the mandrel member 3 is equivalent to the diameter of the die aperture less twice the wall thickness E. In other words, selecting wall thickness E is the same as selecting the diameter of mandrel member 3 since the cross-sectional area of the container, of the die aperture and of the elongated part 1 are predetermined and set for the production of a given extruded part having a wall thickness e and a desired outside diameter.

The extrusion ratio (A) corresponding to the production of wall thickness e when the elongated part 1 cooperates with the aperture of the die 4 is the cross-sectional area of the container less the cross-sectional area of the mandrel part 1 divided by the cross-sectional area of the die aperture less the cross-sectional area of the mandrel'part l. The extrusion ration (8) corresponding to the production of wall thickness B when the mandrel member 3 cooperates with the aperture of the die 4 is the cross-sectional area of the container less the cross-sectional area of the mandrel member 3 divided by the cross-sectional area of the die aperture less the cross-sectional area of the mandrel member 3.

The running pressure for an extrusion is in proportion K with the logarithm of-the extrusion ratio and the overpressure for a diametrally constant mandrel, such as the one graphically represented in FIG. 1, exceeds the running pressure by an amount in proportion Q of the running pressure. Therefore, the selection of the diameter (1) of the mandrel member 3 which then determines wall thickness E for any given product, is made by proportioning the logarithms of the extrusion ratios for production of wall thickness e and E, viz log A and logo, respectively, with the overpressure of a. standard diametrally constant mandrel, viz 1+Q) K logA, and the running pressure of the diametrally constant mandrel, viz K logA. This can be shown as follows:

log A (1+Q)K log A logfi KlogA log A=(1+Q) log 5 And since the extrusion ratio A is established by the desired wall thickness of the final product, it is simply a matter to calculate the extrusion ratio 8 from which the diameter of mandrel member 3, or in the alternate, what the wall thickness E can be determined to result in an extrusion in which the starting pressure does not exceed the running pressure.

The length of part 1 of the mandrel is determined on the basis of the longest expectable ram travel during the upsetting prior to extrusion. The member 3 should have a length equal to at least 5 percent of the length of the part 1. However, the length of member 3 will usually be greater than 5 percent to provide an initial guiding of the extruded product. Furthermore, it should be noted that front member 3 can be applied to part 1 regardless of whether the cross section of part 1 is circular.

Because my invention eliminates overpressure, die wear is reduced such that the. duration of the extrusion can be extended to 10 seconds and by the substitution of a glasslike lubricant with a low viscosity, it is possible to increase the runout velocity to 12 to 15 meters per second. Accordingly, not only does my invention reduce or eliminate the effects of overpressure upon the press itself, but permits the obtention of an extruded product having an increased length over that generally producible with prior art mandrels.

That part of the product which represents an increased wall thickness E, must be cropped off so that a product of uniform thickness e can be obtained. However, the length of the portion that must be cropped off can be limited by properly shaping and positioning the mandrel and, it should be note that 1) the increase in the length extruded in one operation noticeably reduces the relative importance of this cropping, and (2) when the extruded tubes are to be reduced in a stretch reducing mill, a length roughly corresponding to that part has to be cropped on a reduced tube because of the delay needed for starting the stretching effect, even if the extrusion has been conducted in a known manner. Therefore, the method according to the invention does not entail any additional losses.

The following examples illustrate the use of my invention:

EXAMPLE I Use has been made of an extrusion press for steel with a 3,300 short ton force, equipped with a container 232 mm. (9.130 inches) in diameter, a round die 46 mm. (1.810 inches) in diameter and a mandrel with a total length of 870 mm. (34.250 inches). The mandrel had an elongated cylinder section 39 mm. (1.570 inches) in diameter and 750 mm. (29.520 inches) in length. The front end of the elongated section' was the large base of a mm. (0.800 inches) long frustum section, the smaller base of which was 18 mm. (0.710 inches) in diameter, and from which extended a short front member 18 mm. (0.710 inches) in diameter and 100 mm. (4.000 inches) long.

A hollow billet in carbon steel has been inserted into the container, this billet was 220 mm. (8.650 inches) in diameter and 870 mm. (34.250 inches) in length, it had been coated in a known manner with a glasslike lubricant suitable for a high speed of extrusion. This billet has been upset, then extruded in 5 seconds into a 66.2 m. (217 ft.) long tube.

For operating with the known technique, without running the risk of overloading the press, it would have been necessary to contemplate the use of a container 190 mm. 7.480 inches) in diameter, which would have led to place on the ram a stress beyond safety requirements.

EXAMPLE ll Use has been made of an extrusion press for steel with a 1650 short ton force, equipped with a container 148 mm. (5.825 inches) in diameter, a round die 30.8 mm. (1.210 inches) in diameter and a mandrel with a total length of 730 mm. (28.700 inches). The mandrel at its rear end had a 33 mm. (1.300 inches) long frustum, with a 5 angle to the axis and a smaller base 25.3 mm. (1 inch) in diameter. From the small base of the frustum a cylinder of 597 mm. (23.550 inches) long extended. The front end of this cylinder was the larger base of a 20 mm. (0.800 inches) long frustum section, the smaller base of which was 14 mm. (0.550 inches) in diameter. From this frustum section a mm. (3.150 inches) long front cylinder extended which was, of course, 14 mm. (0.550 inches) in diameter. A hollow billet in carbon steel has been inserted into the container, this billet was mm. (4.720 inches) and 29 mm. (1.140 inches) in diameters and 700 mm. (27.600 inches) in length, it had been coated in a known manner with a glasslike lubricant suitable for a high speed of extrusion. This billet has been upset, then extruded in 3.6 seconds into a 40.90 m. (134 ft.) long tube.

The same operation has been repeated nine times without any sign of wear appearing on the die or on the mandrel. The surface condition of the extruded products was excellent as well inside as outside.

On the whole set of extruded tubes, 50 percent of the measured eccentricities were smaller than 3.9 percent, whereas on tubes in the same steel grade and with the same dimensions, extruded in the known manner, 50 percent of the eccentricities would have exceeded 5.5 percent.

If the known manner had been used, it would have been necessary to use a container 126 mm. (5.000 inches) in diameter and only a 500 mm. (20.000 inches) long billet, so that the extruded length would not have exceeded 25 m. (80 ft.)

While I have described the presently preferred embodiments of my invention, it is to be understood that it may otherwise be embodied within the scope of the following claims.

lclaim:

1. In a press including a die having an aperture and a mandrel and which extrudes metals and alloys difficult to deform into hollow products at high temperatures, the mandrel comprising an elongated part having a cross section conforming to the inside configuration of the extruded product; a frontal member having a cross section less than that of the part, said frontal member initially cooperating with the aperture of the die; and a base element joining said member and part together, said cross section of the frontal mandrel member being dimensioned so that the logarithms of the extrusion ratios corresponding to the cooperation with the die, respectively, of said part and of said member are in proportion with the starting pressure and the running pressure of an extrusion carried out with a diametrally constant mandrel, said mandrel resulting in an extrusion operation characterized by a starting pressure which does not exceed the running pressure.

2. A mandrel as set forth in claim 1 wherein the base comprises a frustum having ends that conform to the cross section of the respective member and part to which it joins.

3. A mandrel as set forth in claim 1 wherein the length of the front member is at least 5 percent the length of the elongated part.

4. A mandrel as set forth in claim 1 wherein the frontal member has a circular cross section and said elongated part has a noncircular cross section.

5. In a method for hot extruding metals and alloys into long hollow products with a mandrel having an elongated part and a die comprising the steps of:

A. forming on the mandrel a short frontal member having a cross section significantly smaller than that of the elongated part,

B. dimensioning the cross section of said frontal member so that the logarithms of the extrusion ratios corresponding to the cooperation with the die, respectively, of said part and of said member are in proportion with the starting and pressure and the running pressure of an extrusion carried xl ng a tal d alloys, aid extrusion charact with adiameu-all on t t a d l, terized by a starting pressure which does not exceed the C. positioning the mandrel so that the short frontal member 5 running pressurecooperates with the die at the beginning of the extrusion,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,580,038 Dat d 1971 Jean-Michel Andreassian Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 34, "966,733" should read 966,773 claim 3, Column 4, line 62, "front" should read frontal Signed and sealed this 24th day of August 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents FORM PO-1050(10-69) USCOMM-DC GOSTO'PGQ n u 5. GOVERNMENT PRINTING ornc: I969 0-366-334 

1. In a press including a die having an aperture and a mandrel and which extrudes metals and alloys difficult to deform into hollow products at high temperatures, the mandrel comprising an elongated part having a cross section conforming to the inside configuration of the extruded product; a frontal member having a cross section less than that of the part, said frontal member initially cooperating with the aperture of the die; and a base element joining said member and part together, said cross section of the frontal mandrel member being dimensioned so that the logarithms of the extrusion ratios corresponding to the cooperation with the die, respectively, of said part and of said member are in proportion with the starting pressure and the running pressure of an extrusion carried out with a diametrally constant mandrel, said mandrel resulting in an extrusion operation characterized by a starting pressure which does not exceed the running pressure.
 2. A mandrel as set forth in claim 1 wherein the base comprises a frustum having ends that conform to the cross section of the respective member and part to which it joins.
 3. A mandrel as set forth in claim 1 wherein the length of the front member is at least 5 percent the length of the elongated part.
 4. A mandrel as set forth in claim 1 wherein the frontal member has a circular cross section and said elongated part has a noncircular cross section.
 5. In a method for hot extruding metals and alloys into long hollow products with a mandrel having an elongated part and a die comprising the steps of: A. forming on the mandrel a short frontal member having a cross section significantly smaller than that of the elongated part, B. dimensioning the cross section of said frontal member so that the logarithms of the extrusion ratios corresponding to the cooperation with the die, respectively, of said part and of said member are in proportion with the starting pressure and the running pressure of an extrusion carried out with a diametrally constant mandrel, C. positioning the mandrel so that the short frontal member cooperates with the die at the beginning of the extrusion, and D. extruding said metal and alloys, said extrusion characterized by a starting pressure which does not exceed the running pressure. 